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Old 07-23-2021, 11:07 PM   #1
Junior Member
Join Date: Jul 2021
Posts: 1
Unhappy Communication error HR Neptune HELP Plz

We have a 2005 Holiday Rambler Neptune, Cummins 300 and Allison 1250MH. On way home from 1000 mile trip our service transmission light came on and stop engine. We pulled over, checked fluids and appeared low so we added proper fluids. Lights went off..took a bit but she started shifting right and we traveled a few hundred miles more. Lights come on again and she goes into limp mode. Pull over and check fluids which appear overfull. Drain a bit and limp to Allison certified tech facility. They checked wire harness and find bare wires in throttle position. They believe that caused issues and replace/fix them. While servicing transmission the addressed a few seals that need fixed and notice we need new batteries (house) so they replace those. They had to reprogram valve body to get her in shifting mode after all this but then ACTIVE CODE pops up..apparently it was inactive and has now become active. It says communication error from engine ECM to Transmission ECM. They have put in tester ECM (didn’t fix), check exhaust, batteries, filters, connections and such. Freightliner and Allison help told them to check chassis wire harness and they have checked 8 miles of wires, including chassis wire harness, and found a few bare wires that were addressed. Supposed to get her all put back together on Monday to see if it works..if it doesn’t….we are 85 hours of labor into this..please someone help!!
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Old 07-23-2021, 11:26 PM   #2
Senior Member
Newmar Owners Club
Join Date: Aug 2014
Location: WA
Posts: 281
trans com fail

I have a new Newmar Dutch Star 2019 Freightliner chassis which is now one year old. So I do not know if my experience is pertinent to your situation. It drove fine for the first 10k miles. When I tried to start the engine 2500 miles away from home an error came up "trans com fail". The transmission was not communicating with the engine to tell it what gear it was in and what speed it was going. After a lot for diagnosing by others the Allison tech showed up connected one wire in 5 minutes and it started. After checking for all faults he wired he connected a permanent wire for the transmission with a fuse in it. It was the wiring harness which had lost the wire connection. The coach has gone another 10k miles with no problems.

I hope this helps.
Enjoy the trip and be safe.
Mahdi & Debbie
2019 Dutch Star 4018
2020 Tahoe LT
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Old 07-24-2021, 06:38 AM   #3
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Monaco Owners Club
Join Date: Sep 2014
Posts: 4,280
I'm so sorry to hear about your experience. It sounds like you're closing in on 20k or so.

Unfortunately, these types of problems often require a supertech. Someone that can diagnose and troubleshoot signals. Maybe you can take a little solace in knowing that almost none of us can find a supertech anymore.

Here's to hoping that they'll stumble on the problem and you'll be back on the road. Good luck.
1996 Tioga Class C
2007 Monaco Diplomat 40 PDQ
TOAD 2012 Cadillac SRX 4
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cat, holiday rambler, need help

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